1. Field of the Invention
The present invention relates to a refrigerant compressor for use in a vehicular air conditioning system. More particularly, it relates to a swash plate-type compressor having an improved capacity control response.
2. Description of the Related Art
Referring to FIG. 1, a known swash plate-type variable displacement compressor 50' is provided. One such swash plate-type variable displacement compressor is disclosed in Japanese Patent Publication Hei 4-74549. The shell of compressor 50 ' comprises front housing 8, cylinder block 1, valve plate 2, and rear housing 3. These parts are fixed together by a plurality of bolts 5. Drive shaft 10 extends along the main axis of the compressor 50'. A part of drive shaft 10 is rotatably supported by the front housing 8 through needle bearing 11'. Another part of drive shaft 10 is also rotatably supported by cylinder block 1 through needle bearing 11. Within compressor 50', crank chamber 9 is provided to accommodate rotor 17 and swash plate 19. Rotor 17 is fixed to drive shaft 10 by bolt 14, and rotates together with drive shaft 10. Rotor 17 is coupled to swash plate 19 via variable hinge mechanism 18, so that the tilt angle of swash plate 19 with respect to drive shaft 10 may be changed. Swash plate 19 is connected to center sleeve 22' by pins 40, 40' which are provided in an orthogonal direction with drive shaft 10. Center sleeve 22' is slidably mounted on drive shaft 10 in the axial direction of drive shaft 10. The relative angle between swash plate 19 and center sleeve 22' is variable. Through these connections, when drive shaft 10 rotates, rotor 17, swash plate 19, and sleeve 22' rotate with drive shaft 10. Further, when the capacity of the compressor changes, the tilt angle of swash plate 19 with respect to drive shaft 10 changes, causing center sleeve 22' to slide on drive shaft 10.
Axial movement of drive shaft 10 is inhibited by thrust bearing 41 and adjuster screw 42.
Through shoes 20, swash plate 19 is connected to pistons 13, which are slidably accommodated in a plurality of peripherally-located piston bores 12. When swash plate 19, which is tilted with respect to drive shaft 10, rotates, swash plate 19 rotates with a component of wobbling motion. Since the plane bottom surface of shoes 20 slide on the plane surface of swash plate 19, only the wobbling component of the motion of the swash plate 19 is transmitted to piston 13. As a result, when drive shaft 10 rotates, each piston 13 reciprocates within its piston bore 12.
On one face of valve plate 2, suction valve 15 is attached, and on the other face, discharge valve mechanism 16 is attached. Discharge valve mechanism 16 is fixed on valve plate 2 by bolt 44 and nut 45. Bolt accommodating room 26 is provided at the center portion of the cylinder block 1, and accommodates the head part of the bolt 44.
Within the interior of rear housing 3, suction chamber 4, 4', discharge chamber 6, and known control valve mechanism 21, are provided. Suction chamber 4' is in fluid connection with suction chamber 4, relief passage L1, and control valve mechanism through passage L2.
When compressor 50' is driven to rotate, each piston 13 reciprocates in its piston bore 12, and refrigerant gas from an external refrigerant circuit (not shown) is sucked into suction chamber 4, and compressed refrigerant gas is sent to the external refrigerant circuit (e.g., a condenser) via the discharge chamber 6.
The capacity control of compressor 50' is accomplished as follows. Control valve mechanism 21 has a fundamental function of introducing gas from discharge chamber 6 into crank chamber 9. The gas pressure within suction chamber 4' controls the introduction of gas from discharge chamber 6 into crank chamber 9. The gas within discharge chamber 6 is supplied to control valve mechanism 21 via passage L3. The gas supplied from passage L3 is sent by the gas pressure valance to crank chamber 9 through a control valve (not shown) within control valve mechanism 21, and through passage L4. The suction chamber pressure that regulates the control valve within control valve mechanism 21 is supplied from suction chamber 4', via passage L2, to control valve mechanism 21. The gas in crank chamber 9 exits to suction chamber 4', via relief passage L1.
Thus, the refrigerant gas pressure within crank chamber 9 is determined by a balance between the incoming gas via passage L4 and the outgoing gas via relief passage L1 to suction chamber 4'. Initially, when the refrigerant system is started, the suction chamber pressure within suction chamber 4' is high. In this condition, the control valve (not shown) within control valve mechanism 21 closes to prohibit the introduction of refrigerant gas to crank chamber 9. As a result, the crank chamber pressure does not increase, and the tilt angle of swash plate 19 with respect to drive shaft 10 increases to its maximum by a known mechanism. In other words, compressor 50' operates with the maximum capacity in the initial condition when air within a vehicle compartment is not cool.
As the air within the vehicular compartment cools, the suction chamber pressure within suction chamber 4' decreases. The control valve within control valve mechanism 21 opens in order to allow the introduction of refrigerant gas from discharge chamber 6, via passage L4, to crank chamber 9. As a consequence, the crank chamber pressure within crank chamber 9 increases to the discharge chamber pressure, so that the tilt angle of swash plate 19 with respect to drive shaft 10 decreases to its minimum (in which swash plate 19 is almost perpendicular to drive shaft 10) by a known mechanism.
For a comfortable air conditioning in a vehicular compartment, it is important to have a capacity-reducing response performance, as explained above. It is also desirable for a variable capacity compressor to reduce its capacity quickly when the air in the compartment has been sufficiently cooled. In other words, it is desirable that the crank chamber pressure increases quickly in order to decrease the tilt angle of swash plate 19, so that it is almost perpendicular to drive shaft 10, when the air in the compartment is sufficiently cooled.
However, in known compressor 50', due to the presence of passage L1 with a fixed aperture, a considerable amount of the refrigerant gas in crank chamber 9 constantly returns to suction chamber 4' via relief passage L1. This constant flow of refrigerant gas decreases the rate of rise of the crank chamber pressure within crank camber 9. In other words, the constant flow of refrigerant gas reduces the rate of decrement in the tilt angle of swash plate 19 with respect to drive shaft 10. Thus, known swash plate-type 5 compressors do not show a rapid capacity-reducing ability.